The present invention relates to a moldable heterogeneous composite material having a continuous phase and a discrete phase dispersed in the continuous phase. Preferably, the continuous phase is plastic and the discrete phase is unground rubber. The composite material of the present invention can be molded by providing a flowable melt of a plastic material, providing pieces of unground rubber, mixing the flowable melt of plastic with the pieces of unground rubber to form a composite material, and molding the composite material into a desired shape to form useful articles having high rigidity and good durability.
The disposal of scrap or used tires poses a serious threat to our environment. Unlike other waste products, tires do not readily break down in air or soil. It has been estimated that three billion tires have been discarded into U.S. dumps and land fills. Often, whole tires are simply piled onto vacant space within the dump, creating an eyesore. There, the inner cavities of these tires collect rain water and provide a breeding ground for mosquitoes. As a further hazard, the discarded tires in these piles are often worn to the point where their reinforcing wires are exposed. The exposed wire can injure persons handling the tires or children that attempt to climb the piles.
In other instances, the tires are buried. Chemical reactions between the tires, soil, and air trapped in the cavity can create sufficient heat to ignite the tires, creating a dangerous fire hazard. For these reasons, there have been many attempts to recycle tires into useful products.
Attempts to recycle and reuse tires and other rubber products have focused on several techniques, including reclaiming the rubber through chemical processes, ultrasonic devulcanization, and grinding the rubber prior to mixing it with other components, such as plastics, for subsequent processing.
Reclaimed rubber is defined as the depolymerization product of vulcanized comminuted rubber which retains at least in part the cross links imparted by the vulcanization process of the original rubber. The reclaiming process involves complex and expensive chemical and thermal treatment.
Mixtures of ground rubber and plastic have been used to make molded articles such as automobile bumpers, paving blocks, cable reel drums, and flanges. For example, U.S. Pat. No. 5,733,943, to Doan, discloses a method of making street signs from used rubber tires. The rubber is put through a cryogenic grinding and screening process, then combined with a plastic material to form a moldable mixture. Unfortunately, compositions made with ground rubber lack the strength necessary to be used to mold rigid articles, such as posts and spacers for highway guardrails.
Highway guardrail posts and spacers must be composed of durable material impervious to weathering and resistant to corrosion. They must withstand the impact of flying stones and other debris. They are preferably made of inexpensive, easily manufactured materials. These posts have typically been made of wood, but wood is vulnerable to weathering and can be splintered by flying debris. A durable material which can be used to make highway guardrail posts and spacers is needed.
Used tires and other rubber articles pose a disposal problem. Previous attempts to recycle these articles by grinding or reclaiming the rubber have been complicated and costly. There is a need for a new and significantly improved process for making useful products from used tires and other rubber articles.
It is thus an object of the present invention to provide a moldable composite material having high rigidity that is a combination of plastic and unground rubber.
It is another object of the present invention to provide a molded article formed by a process comprising combining plastic and unground rubber to form a moldable composite material, and molding the composite material to form an article.
It is a further object of the present invention to provide a process for preparing a molded article from the composite material of the present invention.
The foregoing and other objects of the present invention, which shall become apparent as the detailed description proceeds, are achieved by providing a moldable heterogeneous composite material comprising a continuous plastic phase and a discrete phase of unground rubber dispersed in the continuous phase.
Other aspects of the present invention are attained by providing a process comprising providing a flowable melt of a plastic material, providing unground rubber pieces, mixing the plastic material with the rubber pieces to form a heterogeneous composite material, and molding the composite material into an article.
Still another object of the present invention is attained by providing a molded article formed by a process comprising providing a flowable melt of a plastic material, providing unground rubber pieces, mixing the plastic material with the rubber pieces to form a heterogeneous composite material, and molding the heterogeneous composite material to form an article.
Advantageously, pieces of unground rubber cut from used tires and other preformed rubber articles can be combined with thermosetting material, thermoplastic material, or mixtures thereof, to produce a composite material that has high rigidity. This composite material also has good weathering properties and durability. The cut pieces of tire can be used as is, without further processing to remove non-rubber components such as metal. It is not necessary to thermally or chemically treat the rubber prior to use. Expensive cryogenic grinding processes can be eliminated. The large rubber particles give enhanced strength to the composite material. The plastic used can be recycled plastic material. These facts, as well as others, allow this composite material to be molded, using a combination of extrusion and injection molding, into inexpensive, useful articles, such as highway guard rail posts, guard rail spacers, and fence posts.
These and other objects of the present invention, as well as the advantages thereof over existing prior art forms, which will become apparent from the description to follow, are accomplished by the improvements hereinafter described and claimed.